This project is concerned with the development of statistical and mathematical methodology useful in the assessment of risks associated with exposures to potentially hazardous environmental and occupational agents. A major focal point of this effort is the generation of improved statistical techniques for estimating adverse human health effects from laboratory animal data, with particular emphasis being placed on dose-response modeling, low- dose extrapolation and the extrapolation of toxicologic responses across species. Consideration is also given to the modeling of epidemiologic data in the risk assessment process. Current research efforts are concerned with the evaluation of alternative cancer risk models for ionizing radiation, with the implications of a safety factor approach to risk estimation when individual thresholds are present in the exposed population, with the potential relationship between toxicity, genotoxicity and carcinogenicity in laboratory rodents and the possible implications of this relationship for human carcinogenic risk assessment, with an evaluation of the nonlinearity of carcinogenesis dose-response functions, and with the sensitivity of physiologically-based, pharmacokinetic models for estimating the biologically effective dose.